Think of Ukraine from east to west like the USA from north to south: one accent(northern Anglo Saxon) to another (southern Scotts-Irish), with Ukraine being in the middle of a spectrum of Polish > Ukrainian > Mixed( > Russian.
The soviets tried to kill off local languages. And they imported people from Russian peasantry to eastern european cities in order to conquer them just as Western civilization is being conquered by immigration of underclasses from the third world.
In downtown Kiev, everyone speaks both languages – they differ in pronunciation and conventions but are mutually intelligible.
A lot of people outside the cities in ukraine speak “sool’-zhik” which is a mixture of Ukrainian and Russian.
If you spend time in Lviv, then people speak Ukrainian and prefer it.
If you spend time in Donetsk, they speak Russian and prefer it.
Why? Soviets immigrated more people in the east and fewer people in the west. Plus people in the west were previously part of the Polish, Lithuanian and Austrian-hungarian empires, and they have more affinity for european market civilization than authoritarian steppe cultures.